1. Field of the Invention
The present invention relates to a synchronizing signal detecting apparatus of a reproducing apparatus for a video disk or other recording medium.
2. Description of a Prior Art
Conventionally, a digital time base corrector has been practically used which enables a video signal of a corrected time base to be obtained from a reproduced signal of a video disk, for example, having time base fluctuation such as jitter, by writing the reproduced signal in a digital memory in synchronism with the fluctuated time base and reading it with a fixed clock. In such an apparatus, a synchronizing signal drives a character generator for superimposing characters, for example, with an output signal. The synchronizing signal is separately detected in analog form from the video signal of the corrected time base. The reason for this is as follows.
Usually, in a steady state the digital time base corrector detects time base fluctuation not based on a horizontal synchronizing signal of the input video signal but instead based only on a burst signal. Therefore, in the case where the signal is recorded on the disk so that a phase of the burst signal in the video signal is shifted at a portion where a picture is changed to another picture (e.g., a program is changed to another program), or in the case where a burst phase detecting circuit for detecting time base error is locked in a condition shifted by integral times of 360 degrees of the burst phase, the location of the video signal written on the memory for time base correction is changed. Thus, if the character for super-imposition is produced in accordance with a synchronizing signal generated on the basis of a read address of the memory, the location of the character relative to the video signal is changed. Accordingly, it is necessary to detect the synchronizing signal for generating characters not on the basis of the memory address, but instead on the basis of the analog signal converted from the video signal after correcting the time base. This causes a problem in that the size of the circuit becomes large, and it is impossible to process the entire signal digitally.